This invention relates generally to a discharge tube, and more particularly to the type of discharge tube which includes a pair of electrode devices provided in a discharge space in opposed relation to each other, each of the electrode devices being constituted by an arc discharge electrode and a glow discharge electrode.
The Applicant of the present invention has proposed, in Japanese Patent Application Nos. 1-5753 and 2-124177, discharge tubes of the type in which a pair of electrode devices, each composed of an arc discharge electrode and a glow discharge electrode, are disposed in a discharge space in opposed relation to each other. These discharge tubes are used as a back light lamp for a liquid crystal display device, an illumination fluorescent lamp, or the like. As described above, each of the pair of opposed electrode devices of the discharge tube comprises the arc discharge electrode and the glow discharge electrode, and the two electrodes are disposed adjacent to each other. Thanks to the synergistic effect of the arc discharge and the glow discharge, a discharge of an ultra-high brightness can be obtained in a stable manner, so that the discharge tube of an ultra-high brightness can be obtained. And besides, electron-emitting substances, vaporized and emitted in a scattered manner from the arc discharge electrode, are captured by the glow discharge electrode, and since the electron-emitting substances thus captured can be again used for the electron emission, there can be obtained the discharge tube of an extremely long service life.
Recently, there has been provided an arc discharge electrode which is formed by mixing an electron-emitting substance, such as barium, lanthanum boride and cesium, with powder of tungsten, and then by press-molding or compacting this mixture together with a lead wire, using a mold, and subsequently by sintering this compact.